Communication stations can share a communication medium using any of a variety of access techniques. Some access techniques (e.g., carrier sense multiple access (CSMA) techniques) include a contention period in which stations determine contend for use of the medium for transmitting a signal by sensing when the medium is idle. In CSMA techniques, “collisions” sometimes occur when signals from two or more stations overlap. Some CSMA techniques attempt to detect collisions and abort transmission to reduce the negative impact of collisions (e.g., CSMA/CD techniques). Other CSMA techniques include mechanisms to avoid or reduce the probability of collisions (e.g., CSMA/CA techniques). For example, different transmissions may be assigned one of multiple priorities. Access is granted using a Priority Resolution Period in which stations signal the priority at which they intend to transmit, and only the highest priority transmissions are allowed to continue in the contention process. A random backoff mechanism spreads the time over which stations attempt to transmit, thereby reducing the probability of collision.
Other access techniques (e.g., time division multiplexing (TDM) techniques) allocate predetermined time intervals in which certain stations are granted use of the medium. A particular station will transmit within a time slot assigned to that station. In these techniques, a synchronization mechanism is used to ensure that the stations agree about when their slot occurs with respect to a common time reference.